This invention relates to high pressure seals and in particular, but not exclusively, when such seals are being formed between two rigid elements.
There are a number of occasions in which it is necessary to form seals between two engaging metal faces which are being pressed together, but which are subject to significant fluid pressure which is acting in a sense to urge them apart. It is often desirable that these seals are made and remade over a large number of cycles. Previous seals have used a grease such as a silicone based vacuum grease to lubricate the wear surfaces. Such grease is also used when O-rings are provided. In certain instances this grease is undesirable, because cleaning and regreasing can be needed on a regular basis causing down time of apparatus.
One example of such a sealing arrangement is described in WC-A-9308591 wherein a high pressure chamber is being used to process semiconductor wafers. A particular requirement of such an arrangements is that the levels of particulate material must be kept to a minimum.
JP-A-57167568 (Abstract) discloses a metal gasket which does not cause creep at its sealing edge. A relatively thick copper coating is used.
From one aspect the present invention consists in a vacuum or high pressure reusable seal formed between two engaging parts of rigid elements comprising, a coating of a soft metal over at least one of the engaging parts and means for using the parts together. The rigid elements may be formed of steel or aluminum.
The seal may include an underlayer, which may, for example, be nickel. That underlayer may be approximately 2 xcexcm thick. The coating may be between 15 xcexcm and 20 xcexcm thick.
The coating may be gold, silver, platinum, palladium copper, lead or indium, or a combination of these. However, materials such as gold and copper diffuse quite readily into semiconductor materials such as silicon or gallium arsenide and so if the seal is being used in association with a machine for processing such materials, those metals may not be appropriate.
A particularly preferred coating is silver and this coating is suitable for use with semiconductor materials.
The invention also includes a high pressure chamber formed by two closable portions and a seal as defined above.
Although the invention has been defined above, it is to be understood it includes any inventive combination of the features set out above or in the following description.